Philips Hue for VC Enlarging and Safe Light

[MattKing]

You need to be cautious with the above.
The filter settings for the traditional dichroic heads interrelate with the black body spectrum of the lamps - what you end up with is varying amounts of a variety colours of light at the baseboard. It is in no way a pure colour - it is a mixture (in varying amounts) of a number of colours.
The photographic paper is sensitive to that light in varying amounts depending on the colours.
The mixture of colours emitted by the LED light will be different than the mixture resulting from an incandescent lamp being filtered by a dichroic filter.

 

[1kgcoffee]

MattKing,
I'm out of my depth in terms of the physics. Technically lifx bulbs are not dichroic. They are true RGBW. Not unlike my additive Minolta 45a head. So to get Yellow you mix equal parts red and green and to get magenta equal parts red and blue. The light is then mixed together and diffused out from the glass as yellow or magenta. What is the difference?

As halogens age the color of the light also changes and CMY settings also.

I can also say that I've managed to make near identical ra-4 prints from lifx bulb and minolta 45a heads, both additive sources. Only difference being a bit higher contrast and grain due to the collimated light coming out of the condensor. I was having issues at one time with the bulb being too close to the condensor leading to uneven transmission of light. This was fixed by raising the bulb 3/4 of an inch. Never tried a dichroic head to compare.

Here's how the lifx works inside:

 

[MattKing]

For clarity, I'm not commenting on the usability of the various light sources. I'm commenting on calibrating for use an LED source by using the numbers in a chart related to the use of dichroic filters and halogen/tungsten light sources.
Information relating to an additive source would be more useful - provided that the additive source emits the same red, blue and green that the LED source does.
You also need to be cautious when you talk about yellow and magenta when you are considering multigrade/variable contrast black and white printing. The only reason we are used to using magenta and yellow related numbers is that historically those filters were used to filter out colours from a blue and green light containing source like an incandescent/halogen bulb - the yellow filters filter out blue (leaving a greater percentage of green), while the magenta filters filter out green (leaving a greater percentage of blue).

 

[athbr]

A lot of great information here. My understanding of what has been said here so far, please let me know if I'm wrong.

1. Mixing green and blue light instead of yellow/magenta should be fine (considering the bulb would achieve Y/M by mixing in paper safe red this makes sense to me)
2. Colour temperatures corresponds to points on CIE colour space. Therefore, all I need to care about is finding the right HSB values.
3. Most of the guides about colour setting assume different bulbs with different spectral distributions than my LEDs. Only way to find the right values is empirically.

Here's another curve ball. Would some sort of color analyser help me with this? I could measure the light off my enlarger using the standard ilford filters and tungsten lamp then calibrate the LIFX bulb that way.

I've seen everything on ebay ranging from (very expensive) spectroradiometers, handheld colour meters (might only read temperature?) and enlarging color analysers like the Beseler PM2. Anything reasonably priced and easy to find that can help me get a decent readout of my light source?

 

[L Gebhardt]

A lot of great information here. My understanding of what has been said here so far, please let me know if I'm wrong.

1. Mixing green and blue light instead of yellow/magenta should be fine (considering the bulb would achieve Y/M by mixing in paper safe red this makes sense to me)
2. Colour temperatures corresponds to points on CIE colour space. Therefore, all I need to care about is finding the right HSB values.
3. Most of the guides about colour setting assume different bulbs with different spectral distributions than my LEDs. Only way to find the right values is empirically.

Here's another curve ball. Would some sort of color analyser help me with this? I could measure the light off my enlarger using the standard ilford filters and tungsten lamp then calibrate the LIFX bulb that way.

I've seen everything on ebay ranging from (very expensive) spectroradiometers, handheld colour meters (might only read temperature?) and enlarging color analysers like the Beseler PM2. Anything reasonably priced and easy to find that can help me get a decent readout of my light source?

With LEDs you are doing additive color. Each blue or green LED contributes only blue or green (assuming it's perfect). So your light will only be made up of these two wavelengths. With a normal color head it's subtractive. The halogen bulb is a black body radiator and puts out all wavelengths in the visible spectrum. By putting a magenta filter in you are subtracting everything but magenta, and the yellow filter takes out all but the yellow.

Here's a few posts I wrote as I was building my LED head using high power blue and green LEDs. For variable contrast black and white printing you do not need to worry about the color space or color temp meters. But I found it was useful to plot the contrast based on the amount of green and blue so I could set the head to a particular grade / contrast.

 

[DREW WILEY]

I've built and used two true RGB color enlargers, one a huge 8x10 machine, the other for 4x5 and smaller film. Both use banks of halogen bulbs, dichroic filters, and tricky circuitry. It's quite a task, overall. In my opinion, I'd wait awhile before trying this with LED's. The bulb technology is premature, but is gradually evolving that way. You need very precise RGB spectral peaks for accurate color work, and you're simply not going to get it. Making an LED head for selective VC black and white paper printing is more realistic at this point in time.

 

[1kgcoffee]

I've built and used two true RGB color enlargers, one a huge 8x10 machine, the other for 4x5 and smaller film. Both use banks of halogen bulbs, dichroic filters, and tricky circuitry. It's quite a task, overall. In my opinion, I'd wait awhile before trying this with LED's. The bulb technology is premature, but is gradually evolving that way. You need very precise RGB spectral peaks for accurate color work, and you're simply not going to get it. Making an LED head for selective VC black and white paper printing is more realistic at this point in time.

Kodak endura is designed for exposure under LED light and I can say first hand, with all due respect, that the colours in my RA-4 prints are accurate. If I had the spare dough I would send you one to play with. They are marvelous and produce little heat.

I'm beginning to think based on the other responses that pure green, blue and cyan light will do the trick. I think it would be as simple as adding or subtracting 180* from the hue.

 

[MattKing]

For ease of use, add some red light.
It can be a PITA to focus and crop the image from a green and blue only enlarger.

 

[DREW WILEY]

Kodak's and other "digitally optimized" RA4 papers take into account the relative weakness of a green LASER component. LED contact printers do exist in high-volume narrow-roll snapshot machines, but the color output tends to be so-so at best. Awful, in my opinion. Professional results are not expected. Besides, this has little in common with ordinary LED lighting, which is still adolescent. And with all due respect, it takes a LOT more "spare dough" to make a truly effective additive colorhead, although a couple of anemic designs have come out over the years, like the ole rheostatic Phillips tricolor (not to be confused with the junk bulb company), and the impractical Beseler-Minolta flashtube design. Anything with real muscle would cost at least 100K apiece if it had to be commercially sourced today. That's not hypothetical. VC paper doesn't need anywhere near the same degree of spectral precision, so is a much more realistic do-it-yourself target. Part of the problem is that true additive filtration is very dense and needs very high light output, much more so than using CMY subtractive filtration and blackbody white light (LEDs are not blackbody, and at best only fool the eye; they won't fool the narrow spectral peaks of paper dyes). Then you have to figure out how to make all those respective lights selectively "think" together, at least if you are contemplating sequential rather than successive RGB exposure. Sequential is comparatively easy to engineer. You just make three successive exposures to the paper using separate RGB filters. But the specific logistics can be a nightmare. For example, you can't dodge or burn unless you have a pin-registered carrier system with all that in place via a masking system. Automating all that as a simultaneous exposure is a daunting engineering task. I won't go into details. But I guess it all depends on your expectations. I built a couple of additive machines specifically for hue rendition SUPERIOR to any kind of subtractive colorhead. It's hard to imagine any LED experiment getting anywhere near what an ordinary commercial CMY subtractive colorhead can already do, though it might be fun to try.

 

[1kgcoffee]

To each his own. As I have said I cannot readily tell the difference prints made from the Minolta 45a and the led bulb. All the colours pop. I do not have a dichroic head to compare. And unfortunately I cannot find any spectral information on the lifx to have an objective debate.

 

[DREW WILEY]

Like I hinted, any bulb company which claims to produce an LED high CRI bulb, but doesn't offer a published spectrogram is a junk outfit with a high BS coefficient. Doesn't matter. It's the wrong route to an additive enlarger anyway. If intense narrow-band R,G,and B individual LED'S were around, that would be a different story, but you'd still have to figure out how to program them.

 

[1kgcoffee]

I've seen everything on ebay ranging from (very expensive) spectroradiometers, handheld colour meters (might only read temperature?) and enlarging color analysers like the Beseler PM2. Anything reasonably priced and easy to find that can help me get a decent readout of my light source?

Any luck athbr?

 

[athbr]

Any luck athbr?

I just purchased a LIFX bulb and am waiting for it to arrive (I'm not in the US and customs in my country is a nightmare).

As per previous comments I have refrained from buying any tool to analyze colour as it seems like overkill and most are out of budget for me.

I'll resort to testing it out against my set of ilford filters. As long as I can achieve a level 5 contrast with the LEDS it will be fine by hobbiest standards.

I'll be sure to post some test prints when I have them.